This invention relates to a tunnel furnace height detector for detecting whether a height of a ceiling of a tunnel furnace lies in a predetermined allowable range.
When a tunnel furnace has been operated for a long period of time, a ceiling of the furnace is likely to lower due to deterioration of the furnace body. Therefore, the height of the tunnel furnace has to be inspected periodically. Such an inspection of the ceiling has been effected after operation of the furnace was shut down and the furnace temperature has been allowed to cool completely. In another case, a fiber scope is inserted through a furnace wall into the furnace to observe the lowering of the ceiling of the furnace. For example, there have been cameras utilizing optical fibers as fiber scopes, which are able to observe objects in high temperature atmospheres by cooling the cameras from an outside of the furnace by cooling water.
However, the shut down of the operation of the tunnel furnace for periodic inspection of ceiling height unavoidably lowers its production efficiency in continuous operation. On the other hand, the observation of the ceiling height by the use of fiber scopes can not numerically detect the lowering of the ceiling. Moreover, rapid lowering of the ceiling can not be detected by such conventional means, and in extreme cases therefore, there was a risk of the ceiling being falling, resulting in a terrible accident.